1. Field of the Invention
The present invention relates to a data storage system used for an external storage device of a computer, data storage control device, and write error diagnosis method for the disks thereof, and more particularly to a data storage system in which many disk devices and a control device are connected via transmission paths, data storage control device, and write error diagnosis method for the disks thereof.
2. Description of the Related Art
Today as various data are computerized and handled on computers, the importance of data storage devices (external storage devices) which can store large volumes of data efficiently with high reliability, independently from a host computer which executes data processing, is increasing.
As such a disk storage device, a disk array device has many disk devices (e.g. magnetic disks, optical disks) and a disk controller to control these many disk devices, is being used. This disk array device can simultaneously accept disk access requests from a plurality of host computers, and perform control for many disks.
Such a disk array device has an internal memory which plays a role of a cache of the disk. By this, the data access time, when a read request or write request is received from the host computer, can be decreased, and higher performance can be implemented.
Generally a disk array device has a plurality of major units, that is a channel adapter which is a part connecting the host computer, a disk adapter which is a part connecting the disk drive, a cache memory, a cache control section for controlling the cache memory, and many disk drives.
If a failure occurs to a unit of the disk drive in this complicated system, the failure must be detected. One failure is that data cannot be written on the disk normally when the write command is issued to the disk drive. For example, to quicken the write speed of the disk drive, the disk drive writes the data on the disk and reports write completion without executing the read verify operation unless a special command is issued. Therefore in some cases data may not be written normally on the target track, because of the deterioration of the head or due to influence on adjacent tracks. This is called a “write miss error”.
Because of this, diagnosis is required for the write data on the disk. A conventional method for this is that the control device issues a write data with attaching CRC (Cyclic Redundancy Code), to the disk drive, and the disk drive writes the write data to the disk along with the CRC. When write completion is reported, the control device reads the CRC from the disk and compares it with the CRC attached to the write data to diagnose the write error (e.g. Japanese Patent Application Laid-Open No. H5-166304).
Another prior art is that when write data is distributed and written to a plurality of disk drives which makeup a RAID configuration, time stamp information is attached to the distributed write data, and is transferred to the disk drive, and the disk drive writes the write data on the disk along with the time stamp information. When the read command for this data is received from the host, the control device reads the distributed write data from the plurality of disk drives, checks the time stamp information in the distributed write data, determines the normal time stamp information based on a majority decision, and judges the disk drive having other time stamp information as abnormal (e.g. Japanese Patent Application Laid-Open No. H10-171608).
However in the case of the former prior art, if the CRC of old data before writing the disk and that of new data happen to be the same when the new data overwrites the old data, it cannot be diagnosed whether the new data was written correctly.
Since the latter prior art is a method for detecting a failure of one disk drive based on the data of the plurality of disk drives, an individual disk drive cannot be diagnosed directly. For example, if the time stamp information of the read data of two disk drives, out of three disk drives, match, it is judged that the other one disk drive has a failure, so if a write miss error occurred to the two disk drives, then the other disk drive, which is normal, is judged as a failure.
Also since a time stamp holds write time information, the control device cannot diagnose a write miss error by comparing the time when the data was written with the present time, since the time is always different regardless whether the disk drive is normal or abnormal.